The field is ventilation, i.e., the art of removal or renewal of gas in a closed space, room, or container. The invention offers a method to ventilate a space, room, or container that has only one opening or venthole and can, therefore, not be flushed. The method may be used even if the space is filled with solids such as granular material.
The invention is based on two prior U.S. Pat. Nos. 4,770,675; 5,288,169 and on a number of publications listed above.
These patents and papers describe a method by which the diffusional mass transport of a tracer substance within a carrier fluid is enhanced by several orders. The method was first presented by Taylor (1953) for the mass transport of a tracer in steadily moving fluid. More recently, the phenomenon was applied to oscillatory flow in pipes (Harris and Goren, 1967; Watson, 1983; Jaeger and Kurzweg, 1983). The theory was substantiated by experiments (Joshi C H, Kamm R D, Drazen J M and Slutszky A S, 1983). The mass transport maintains its diffusional character which has led to its application to separating gases or solutes. Optimal conditions may be achieved that give maximal mass transport and maximal separation (Kurzweg U H and Jaeger M J, 1986, Jaeger M J, 1998).
The mechanism responsible for this enhanced transport is due to the interaction of two well known fundamental physical properties. The first is related to fluid viscosity: when fluid flows steadily in a pipes the fluid near the pipe wall is slowed down while the fluid in the pipe""s centerline is accelerated. The second is molecular diffusion: molecules move from an area of high concentration to an area of low concentration due to random thermal motions. The property of molecular diffusion is maintained when the fluid is flowing which allows the two mechanisms to interact. Thus, molecules located in the fast flowing center region may diffuse radially toward the sluggish boundary layer and molecules from the motionless boundary layer may diffuse into the fast streaming center region. In oscillatory flow the process becomes rather complex, with radial motions toward the centerline and away from the centerline occurring alternatively. The process depends on pipe radius, oscillation frequency, and physical properties of the carrier and of the tracer molecules. It results in greatly increased mass transport down a concentration gradient as shown by Watson, 1983, Jaeger and Kurzweg, 1983 and Kurzweg and Jaeger, 1986. An interesting property of the process is that it maintains its diffusional character, i.e. molecules of different size move at different speeds U.S. Pat. No. 4,770,675; Jaeger M J, 1998).
The dispersion process is also observed in porous media where it has been studied extensively for its industrial applications using packed columns. A summary of the extensive work is found in monographs by Leva (1959) and Bear (1972). The mechanism in those media is typically different from that in tubes. Convective mixing of parallel rivulets becomes increasingly important. The process is not accessible to a rigorous analytical solution. Approximations have been published and summarized by Bear (1972). Recent work by Hall (1995) indicates that these early studies, done on steady laminar, porous flow, are valid as well in oscillatory, porous flow.
The present invention is based on above processes. In addition, it makes use of a third fundamental property, namely gas compressibility. The invention is therefore only applicable to gases. To our knowledge the adding and withdrawing repeatedly volumes of gas with the intention of ventilating a gaseous space has been used only once before, namely by Neeper in his 1994 U.S. Patent. The invention describes the pumping and withdrawing of volumes of air into the ground for the purpose of purging the ground of volatile contaminants such as gasoline. The present invention differs from Neeper""s by its geometry and by its applications, yet is based on the same principles.